Liquid crystal display devices are devices that control the transmission or blockage of light (turning ON/OFF the display) by controlling the orientation of liquid crystal molecules having birefringence. Examples of liquid crystal orientation modes of LCDs include the twisted nematic (TN) mode in which liquid crystal molecules having positive dielectric anisotropy are oriented so as to be twisted at 90° when viewed from a direction normal to the substrate, vertical alignment (VA) mode in which liquid crystal molecules having negative dielectric anisotropy are oriented vertically with respect to the substrate surface, and in-plane switching (IPS) mode and fringe field switching (FFS) mode in which a horizontal electric field is applied to liquid crystal layer to orient liquid crystal molecules having positive or negative dielectric anisotropy horizontally with respect to the substrate surface.
As a method of driving a liquid crystal display device, the active matrix driving method, in which active elements such as thin film transistors (TFTs) are disposed for each pixel and a high image qualities is attained, is popular. On an array substrate including a plurality of TFTs and pixel electrodes, a plurality of scan signal lines and a plurality of data signal lines are formed to intersect each other, and a TFT is provided at each intersection. The TFT is connected to the pixel electrode, and the switching function of the TFT controls the supply of an image signal to the pixel electrode. A common electrode is further provided on the array substrate or an opposite substrate, and a voltage is applied to the liquid crystal layer through the pair of electrodes.
In IPS mode, which is a mode in which the orientation of liquid crystal molecules is controlled by a horizontal electric field, the pixel electrodes and the common electrodes are formed on the same substrate, and both electrodes have a plurality of teeth. The teeth of the pixel electrodes and the teeth of the common electrode are parallel to each other, and the orientation of the liquid crystal molecules is controlled on the basis of a potential difference between the teeth of the pixel electrode and the teeth of the common electrode (see Patent Document 1, for example).
In the IPS mode described above, the pixel electrodes and the common electrodes are typically formed on only one of the pair of substrates, but another electrode may be formed on the opposite substrate, and in some cases, the orientation of the liquid crystal molecules is controlled not only by a horizontal electric field but also by a vertical electric field or an oblique electric field (see Patent Documents 2 to 4, for example).